In a system that plural apparatuses mutually perform data communication, it enables to prevent decrease in productivity and to smoothly operate the entire system. In the system, when data received from an image data generation apparatus through a data communication medium is image data, acceptance from other image data generation apparatus is invalidated, and a printing process for the image data from the image data generation apparatus is performed. According as the data received from the image data generation apparatus through the data communication medium is first information output when an error occurs in the image data generation apparatus and representing this error, the invalidation of the acceptance from the other image data generation apparatus is released.